In a cell based wireless communication system, a coverage hole is generated because of a local characteristic of an environment of each area, a building, etc. In order to address this, a repeater is additionally installed for a service. However, there is a problem that the repeater causes performance deterioration resulting from noise amplification.
So, as an evolved type of the repeater, a Relay Station (RS) not simply amplifying but decoding and forwarding a signal from a Base Station (BS) has been proposed.
This RS is being actively researched for the purpose of the improvement of a throughput of a cell based wireless communication system and the expansion of a coverage. A standardization work for practical use is underway in the Institute of Electrical and Electronics Engineers (IEEE) 802.16j.
An RS system now taken into consideration in IEEE 802.16j and RS related research field is of a half duplex mode. The RS system is of a structure of not simultaneously performing reception and transmission within the same frequency resource region but dividing time and performing only one operation at a time.
In this case, there is a need for two signal transmissions such as signal transmission on communication between a BS and an RS and signal transmission on communication between the RS and an MS.
Compared to a single hop system, this inevitably requires twice of resource consumption and reduces spectrum efficiency, and additionally requires a transmission/reception switching time of the RS.
Also, at a BS standpoint, there is a problem that ineffectiveness having to separately transmit broadcast information for the RS occurs, and an UpLink (UL) coverage of single hop users serviced by the BS reduces because of dividing and using an RS link and an access link by time.
In order to address these problems, a structure in which an RS simultaneously performs transmission and reception using two antennas has been proposed. The RS performing this is called a full duplex RS.
However, a full duplex RS system has a problem that a standard support technology development for this and a research on a case to coexist with a half duplex RS system are unsatisfied.
In actual, a transmit signal fed back from a transmit antenna is distorted by a characteristic (i.e., non-linearity, etc.) of an Intermediate Frequency (IF)/Radio Frequency (RF) device including an amplifier and the transmit signal is received by a receive antenna. Thus, no matter how accurate interference channel estimation is, the transmit signal cannot be eliminated perfectly.
That is, an antenna interference signal of a full duplex RS not includes only a transmit signal but includes an EVM. The EVM is a transmit end error generated while passing through an IF, an RF, an amplifier, etc by a variety of kinds of a non-linear distortion, a Common Phase Error (CPE), an Inter-Modulation Distortion (IMD), etc.
An error generated at a transmit end in this manner is generically called an EVM. The EVM can vary depending on an IF/RF characteristic of the maximum transmit power, the maximum resource allocation size, a CPE, etc., and an amplifier characteristic such as back-off, etc. That is, the EVM varies depending on IF/RF and amplifier non-linear characteristics of a full duplex RS, a resource allocation region in full duplex, a back-off value of an amplifier according to the maximum transmit power, and a CPE/IMD improvement algorithm. And, the EVM corresponds to a component, which cannot be estimated and eliminated, among RS transmit signals and thus, becomes a factor limiting interference cancelation performance.
Accordingly, there is a problem that, if the BS determines only a full duplex support or non-support in an RS initial access process and working process, it cannot determine the maximum resource allocation region allocatable to the full duplex RS and, if the BS performs power control without considering an EVM, the full duplex performance of the RS is deteriorated.
Particularly, as a transmit power of an RS and a resource allocated to the full duplex RS increase, an EVM also increases and therefore, there is a problem that, although a feedback interference of a transmit signal is canceled through an interference cancelation algorithm, upon receipt of a signal from the BS, performance deterioration may occur.
Accordingly, there is a need for an initial negotiation procedure and a message exchange process during operation in which, in order to efficiently operate, a full duplex RS measures an EVM of a transmit signal not eliminated depending on a transmit power and a resource allocation size and a BS determines the maximum transmit power and the maximum resource allocation size.